Elemental sulfur production in hydrometallurgy
Section D-Review
ELEMENTAL SULFUR PRODUCTION IN HYDROMETALLURGY Fathi Habashi
Keywords: Sodium sulfide; Oxidative leaching; Sulfide ores; Surface active agents; Gold; Mercury. Elemental sulfur obtained during oxidative leaching of sulfides at low temperature will contain mercury and gold and both can be effectively recovered using sodium sulfide. Other metals go into solution.
* Corresponding Authors: E-mail:
[email protected] [a] Department of Mining, Metallurgical, and Materials Engineering, Laval University, Quebec City, Canada
INTRODUCTION When sulfide minerals are treated in acid medium and in oxidizing atmosphere elemental sulfur forms while the metals goes into solution (Figure 1).1 There is a narrow region where elemental sulfur can form (Figure 2).
Figure 2. Formation of elemental sulfur during oxidizing sulfide ores at 100oC
Figure 3. Left: Molten sulfur covers sulfide surface in absence of surface active agent. Right: Molten sulfur does not cover sulfide surface in presence of surface active agent
Figure 1. Recovery of metals in sulfide ores below the melting point of sulfur
SPECIAL CASES Sulfides containing gold
This region disappears above 150 oC. Sulfur melts at 119.5 oC and polymerizes at 160 oC. If the treatment is conducted below 150 oC a surface active agent must be present to prevent the molten sulfur from impeding the reaction by forming a protective layer on the sulfide particle (Figure 3).2
Eur. Chem. Bull., 2017, 6(9), 424-425
Sulfide ores may contain gold embedded in the sulfide matrix and as a result many gold producers treat such ores at high temperature to liberate gold then treating the residue containing gold by cyanidation to recover gold.3 It was found that gold will be associated with the sulfur.
DOI: 10.17628/ecb.2017.6.424-425
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Elemental sulfur production in hydrometallurgy
Section D-Review
Jeffrey and Anderson4 and Anderson and Twidwell5 found that sulfur formed agglomerates containing all the gold as well as unreacted sulfides. Cyanidation of these agglomerates was not effective in recovering gold but sodium sulfide was. This can be conducted by leaching the agglomerates in sodium hydroxide whereby sodium sulfide was formed: 4So + 6NaOH → 2Na2S + Na2S2O3 + 3H2O (x-1)So + Na2S → Na2SX
(where x = 2 to 5)
CONCLUSION While metals in sulfide ores go in solution as elemental sulfur forms, gold and mercury are embedded in the sulfur and can be recovered by leaching with sodium sulfide provided a surface active agent is present.
REFERENCES F., A Textbook of Hydrometallurgy, Métallurgie Extractive Québec, Québec City, Canada 1993, second edition 1999. Distributed by Laval University Bookstore, www.zone.ul.ca
1Habashi,
Gold dissolution was the result of leaching by polysulfides and sulfides:
L. and Dreisinger, D. “Interfacial Properties of Liquid Sulfur in the Pressure Leaching of Nickel Concentrate”. Miner. Engg., 2009, 22, 456–461, https://doi.org/10.1016/j.mineng.2008.12.003
2Tong
2Au + S2 + 2S → 2AuS +2S 2-
2-
-
2-
Gold was recovered from solution by including electrowinning, gaseous precipitation, chemical precipitation, cementation, solvent extraction and ion exchange. Sulfides containing mercury
Habashi, F. Gold. History, Metallurgy, Culture, Métallurgie Extractive Québec, Québec City, Canada 2009. Distributed by Laval University Bookstore, www.zone.ul.ca
3
M. and Anderson, C. G. “A Fundamental Study of the Alkaline Sulfide Leaching of Gold”, European Journal of Mineral Processing and Environmental Protection, October 2002
4Jeffrey,
C. G. and Twidwell, L. G. “The Alkaline Sulfide Hydrometallurgical Separation, Recovery and Fixation of Tin, Arsenic, Antimony, Mercury, and Gold”, pp. 121-131 in Lead and Zinc 2008, Southern African Institute of Mining and Metallurgy
5Anderson,
6
Jorjani and Ghahreman reported that if mercury is present in the ores the elemental sulfur will contain the mercury and this can be leached by sodium sulfide to free it from mercury by forming insoluble mercury sulfide while elemental sulfur forms soluble polysulfide: Na2S + (x−1)S° → Na2Sx
E. and Ghahreman, A. “Elemental Sulfur Removal during the Leaching of Copper and Zinc Sulfides, and from the Residues; A Review”, Hydrometallurgy 2017, 171, 333-343 https://doi.org/10.1016/j.hydromet.2017.06.011
6Jorjani,
Hg2+ + S2- → HgS In conclusion, it is obvious therefore that elemental sulfur obtained during oxidative leaching of sulfides will contain mercury and gold and both can be effectively recovered using sodium sulfide.
Eur. Chem. Bull., 2017, 6(9), 424-425
DOI: 10.17628/ecb.2017.6.424-425
Received: 03.09.2017. Accepted: 07.10.2017.
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